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Robin Hamblett
United Kingdom
534 Posts |
 Posted - 26/10/2009 : 10:53:45
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Mike Hawke's wonderful book "75 Years of the J2 M.G." page 22 carries Modification during production. On 8/9/33 from Chassis J3576 the Speedo drive ratio was changed. Anybody know from what and to what please? I presume this also implies a change of speedo unit as well so same question applies.
Thanks
Robin |
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JMH
United Kingdom
911 Posts |
Posted - 26/10/2009 : 12:29:13
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Robin,
Straight from the man himself (& off the top of his head, which was quite impressive); the original ratio was 8:14. The change was necessitated by the re-routing of the speedo cable & also involved the fitting of an angled drive to the back of the speedo itself. Whilst he couldn't recall directly what the new ratio was, it could be in "Blower". I expect I'll get a further call when he gets off gardening duty.
JH |
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Peter Green
United Kingdom
1682 Posts |
Posted - 26/10/2009 : 14:55:55
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Jeremy,
Was not the angle drive a 1-1 ratio? If so that would not have necessitated a change of gearbox ratio.
Peter. |
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Mike Allison
United Kingdom
196 Posts |
Posted - 26/10/2009 : 15:23:45
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Hi all,
I think the speedo pinion was changed to a P-type ratio. Certainly the speedos themselves are different. The speedo drive ratio is stamped (eg 8/14 for the J) onto the casing of the gearbox, ahead of the remote control, and can easily be read with the bonnet open... except for cars fitted with an under-bonnet toolbox!
Who said MG's were simple to maintain?
Best wishes,
Mike |
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JMH
United Kingdom
911 Posts |
Posted - 26/10/2009 : 19:25:53
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Robin,
The info in the book came from the original factory spare parts list (I think you can get a repro from Mike Dowley). It also confirms the speedos as different. If Peter thinks the angle boxes are 1:1, then we need someone lucky enough to have the 2 original types on the shelf to do a direct comparison for the exact differences.
JH |
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patrick henry
United Kingdom
116 Posts |
Posted - 26/10/2009 : 20:56:56
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Robin
The early J2s up to chassis 3576 were fitted with Smiths governor type speedos (Smiths code PB) these had a speedo cable ratio of 2240 cable turns per mile which corresponded with the standard 8/14 teeth on the cable drive gears in the gearbox .
After chassis number 3576 the J2s were fitted with the L-Type chronometric type speeedo(with multi coloured face) which had a ratio of approx 1600turns of the cable per mile.
Late J2s and L-Types were originally fitted with a small external gearbox which screwed into the drive on the gearbox to correct the different ratios.
So to enable a chronmetrics speedo to work correctly on a J2/L-type it would need either an external type cable gearbox fitting or the gearbox drive gears would need changing to the standard P-Type 4/10 speedo gears(All P-Types had chronometrics as standard)
Regards Patrick
pchenry |
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Peter Green
United Kingdom
1682 Posts |
Posted - 26/10/2009 : 23:10:48
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My previous posting is a bit missleading, the angle drive I was refering to is the one that is fitted to P and N types which has a 1-1 ratio.
On looking through the J type parts list I see that the later J types had a reduction box to cater for the different speedo unit, this change commenced at chassis number J3576, the reduction box is quoted as having a ratio of 100/143. There is no mention of the 8/14 gearbox speedo drive ratio changing at all.
Peter. |
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Robin Hamblett
United Kingdom
534 Posts |
Posted - 27/10/2009 : 10:58:35
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Thanks to all on this.
My car, J3666, has the multi coloured chromo' speedo as per Patrick's posting. My issue, as such, is that is was calibrated to go with my old P type engine and box. Now I have reverted to a correct J engine and box, with J ratios and direct drive to the speedo, the speedo is reading over the odds by some margin. e.g. 30mph actual reads as 52mph on the speedo!
Sounds like I need a recallibration and a reduction box as the easier option to pulling the box out and changing the pinion and gear.
Any ideas Patrick on what to do next?
Thanks
Robin
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tholden
United Kingdom
1638 Posts |
Posted - 27/10/2009 : 13:22:47
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Robin if you give me a call this evening I can direct you to someone who can help with this.
TH |
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LewPalmer
USA
3242 Posts |
Posted - 27/10/2009 : 22:29:50
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Could someone please send me a photo of the late J2 tach face (as straight on as possible? I am in the process of doing the artwork for production of replacement dial faces and need a good photo.
TIA,
Lew Palmer
Registrar, NAMMMR |
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George Eagle
United Kingdom
3237 Posts |
Posted - 28/10/2009 : 11:38:17
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Hi Lew
I have emailed you a photo. Hope it helps you.
Regards George
quote:
Originally posted by LewPalmer
Could someone please send me a photo of the late J2 tach face (as straight on as possible? I am in the process of doing the artwork for production of replacement dial faces and need a good photo.
TIA,
Lew Palmer
Registrar, NAMMMR
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PaulusPotter
Netherlands
202 Posts |
Posted - 28/10/2009 : 12:10:47
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Hello George,
Hope you do not mind to put the photograph on this site to enable all to see it. For people like me, new in Triple M heaven, it is very helpfull. For now and for later as back up for all your knowledge
Thanks.
Paul |
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Terry Andrews
United Kingdom
546 Posts |
Posted - 29/10/2009 : 10:58:58
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My L1 Continental Coupe has these parts fitted as it left the factory.  As Pat says the reduction box is fixed directly to the gearbox. It is round and has offset out put and is of similar construction to these you see on the back of dynamos on TDÆs, TFÆs etc. There is no provision for a right angle drive as with the P / NÆs. Sorry I have not taken a specific image of this yet. I attach a picture of the original face associated with the reduction box.
Paul, As you are using a P/N gearbox with an overdrive you will not need one of these reduction boxes but another solution depending how you go with your instruments. I will explain this to you when we and the other L CC owners meet up in Holland on Wednesday. Regardsà.. Terry
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LewPalmer
USA
3242 Posts |
Posted - 29/10/2009 : 11:38:25
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Thanks, Terry.
Lew Palmer
Registrar, NAMMMR |
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